Valid Thursday January 24, 2019 to Monday February 04, 2019

Synopsis: A strong area of upper-level low
pressure is forecast to persist across the eastern half of North America
through at least the end of January. Multiple outbreaks of Arctic air are
likely to overspread the central and eastern U.S. during the next ten days. A
low pressure system is forecast to exit the Northeast on Thursday. A surface
low may develop across the northeast Gulf of Mexico this weekend and strengthen
as it tracks northeast near the mid-Atlantic coast. Upper-level high pressure
is likely to strengthen over Alaska and shift slightly westward towards the
Bering Sea during Week-2.

Hazards

Much below normal
temperatures shifting southeast from the northern Great Plains and upper
Mississippi Valley to the Southeast, Thu-Fri, Jan 24-25.

Much below normal temperatures across much of the central and eastern U.S.,
Sat, Jan 26.

Much below normal temperatures shifting south across the Great Plains, Mon,
Jan 28.

Severe Drought across parts of the Florida peninsula, Southwest, central to
southern Rockies, Great Basin, California, and Pacific Northwest.

Detailed Summary

For Thursday
January 24 - Monday January 28: The major hazard during the final week of
January is likely to be much below normal temperatures as Arctic high pressure
continues to shift south from Canada. On Thursday and Friday, Arctic high
pressure (1038 to 1042-hpa) is forecast to shift southeast from the northern
Great Plains to the Ohio and Tennessee Valleys. This Arctic surface high is
then expected to overspread the eastern U.S. by Saturday. The much below normal
temperatures hazards are depicted for areas where daily temperatures are most
likely to average 10 to 20 degrees F below normal. Dangerously low wind chills
are likely to accompany this Arctic outbreak later this week. The coldest
temperatures (-25 to -10 degrees F) are forecast across the northern Great
Plains, Midwest, and upper Mississippi Valley on Friday morning. Frost and/or a
light freeze may extend as far south as the northern Florida peninsula on
Saturday morning.

On Thursday, the deterministic 6Z GFS and 0Z ECMWF models are in good
agreement that a surface low strengthens as it tracks north from the
mid-Atlantic to New England. Warm air advection during the next few days is
expected to result in much of the precipitation falling in the form of rain
across the mid-Atlantic and Northeast. Although accumulating snow is expected
from the central Appalachians and interior Northeast on the backside of the
surface low, total snowfall amounts are not anticipated to be hazardous at this
time.

The next potential for winter weather hazards begins this weekend across
the Southeast as a shortwave trough in the northern stream possibly amplifies
near the Gulf Coast. The deterministic 0Z ECMWF is the sharpest with this
shortwave trough and depicts a rapidly strengthening surface low tracking from
the northeast Gulf of Mexico to the Outer Banks. This model solution poses a
risk for heavy snow across interiors areas of the eastern U.S., as far south as
Alabama and Georgia. However, the deterministic GFS model runs are weaker with
the 500-hpa shortwave trough and its associated surface low. Spread among the
6Z GFS ensemble members is large, but a few members support the deterministic
0Z ECMWF with a high impact winter storm for the eastern U.S. Due to low
confidence with such large ensemble spread, no heavy snow hazard is depicted at
this time but this will be closely monitored in the hazards outlooks during the
next few days.

Another Arctic high is expected to shift south from Canada into the Great
Plains by Monday. Therefore, much below normal temperatures are forecast to
return to parts of the Great Plains, upper Mississippi Valley, and Great Lakes
on Jan 28.

The latest GFS model runs feature a 968-hpa surface low near Kodiak Island
on Friday. Enhanced onshore flow with a subtropical connection is likely to
result in heavy precipitation (coastal rain and high-elevation snow) on Jan 25
and 26 across the Kenai Peninsula, southeast mainland Alaska, and Alaska
Panhandle. A strengthening upper-level ridge is likely to result in a much
drier pattern for Alaska by the Week-2 period.

For Tuesday January 29 - Monday
February 04: The ensemble means maintain a highly amplified longwave
pattern over North America into the beginning of February. A notable trend in
the model solutions during the past few days is for a slight retrogression of
the upper-level pattern with the amplified ridge shifting from the West Coast
of North America west to the north Pacific and Bering Sea. This slight
retrogression would result in lower 500-hpa heights across the interior West
with time and an increase in 500-hpa heights across the Southeast. Given the
good model agreement and continuity supporting a moderating trend later in
Week-2, the slight risk for much below normal temperatures along the Gulf Coast
and across the Southeast is discontinued after February 1.

A high risk (60 percent chance or higher) of much below normal temperatures
(lowest 15th percentile of the climatological minimum temperature distribution)
is forecast across the north-central U.S. early in Week-2. The GEFS
probabilistic temperature tools indicates that there is a 20 to 40 percent
chance of record cold temperatures across the Midwest and Ohio Valley from
January 29 to 31. A slightly broader area is covered by a moderate risk of much
below-normal temperatures during the entirety of Week-2 due to the expectation
for a gradual westward transition of anomalous cold with time.

Although there are no precipitation hazards posted during Week-2, there is
an increased risk of freezing rain with any overrunning precipitation that
develops given the well established Arctic air over the central and eastern
U.S. at the beginning of Week-2. The most likely area for freezing rain would
be from the south-central Great Plains east to the Tennessee Valley and
southern mid-Atlantic. As the upper-level ridge shifts northwest to Alaska, the
southern stream may become more active late in Week-2. At this time, no
specific precipitation hazards can be identified.

The U.S. Drought Monitor, valid January 15th, shows slight improvement of
severe drought (D2-D4) conditions in the U.S, down from 10.50% to 10.02%. These
improvements occurred across southern Colorado and southern
California.